The present invention relates to telescopic gunsights, and more particularly to telescopic gunsights and associated equipment used to achieve shooting accuracy at extreme ranges.
All shooters, whether they are police officers, olympic shooters, or weekend enthusiasts, have one common goal: hitting their target accurately and consistently. Accuracy and consistency in shooting depend largely on the skill of the shooter and the construction of the firearm and ammunition.
The accuracy of a firearm can be enhanced by the use of precisely-made components, including precisely-made ammunition. It is well known in target shooting that using ammunition in which the propellant weight and type, bullet weight and dimensions, and cartridge dimensions are held within very strict limits, can improve accuracy in shooting.
At very long ranges, in excess of 500 yards, however, the skill of the shooter and the consistency of the ammunition is often not enough to insure that the shooter will hit the target. As range increases, other factors can affect the flight of the bullet and the point of impact down range. One of these factors is xe2x80x9cbullet dropxe2x80x9d. xe2x80x9cBullet dropxe2x80x9d is caused by the influence of gravity on the moving bullet, and is characterized by a bullet path which curves to earth over long ranges. Therefore to hit a target at long range, it is necessary to elevate the barrel of the weapon, and the aiming point, to adjust for bullet drop. Other factors, such as wind, magnus effect (i.e., a lateral thrust exerted by wind on a rotating bullet whose axis is perpendicular to the wind direction), bullet design, and the idiosyncracies of the weapon can cause the bullet to drift to the left or right of the central path of the bullet over long range. Such effects are generally referred to as xe2x80x9cwindagexe2x80x9d effects. Therefore, to hit a target at long range, it may be necessary to correct for windage by moving the barrel of the weapon slightly to the left or the right to compensate for bullet drift. Thus, in order to hit a target at long range, the shooter must see the target, accurately estimate the range to the target, estimate the effect of bullet drop and wind on the bullet, and use this information to properly position the barrel of the firearm prior to squeezing the trigger.
Conventional telescopic gunsights or scopes are not generally useful at long ranges in excess of 600-800 yards. The cross-hairs of such scopes are typically located in the center of the field, with the vertical hair providing a central indicator for making a windage adjustment, and the horizontal hair providing a central indicator for making a bullet drop adjustment. Modifications to this basic system have not, thus far, enabled a skilled shooter firing at long ranges to acquire and hit a target quickly and reliably, regardless of the weapon used (assuming always that the weapon is capable of reaching a target at the desired long range).
For example, U.S. Pat. No. 1,190,121 to Critchett, discloses a reticle for use in a rifle scope containing a rangefinder having markings for finding a range with reference to the height of a man. Apparently because of the innate variation in the height of any given individual from that used to produce the reticle, and the resulting inaccuracy which that would produce at long ranges, Critchett""s scope was only useful to 600 yards.
U.S. Pat. No. 3,948,587 to Rubbert discloses a reticle and telescope gunsight system having primary cross-hairs which intersect conventionally at the center of the field, and secondary horizontal cross-hairs spaced apart by different amounts to form a rangefinder and distinct aiming apertures and points, based upon a predetermined, estimated size of a target. Rubbert""s preferred embodiment is constructed for use in shooting deer having an 18xe2x80x3 chest depth. However, like Critchett, the usefulness of Rubbert for shooting other targets of varying size at long range is doubtful.
U.S. Pat. No. 3,492,733 to Leatherwood discloses a variable power scope having aiming cross-hairs and two upper cross-hairs for bracketing a target of known dimensions at a known distance. The scope is mounted to a gun barrel, and the position of the scope in relation to the gun barrel is adjustable up and down to compensate for bullet drop by covering the target with the bracketing cross-hairs, and rotating an adjustment ring to expand or contract the bracketing cross-hairs to bracket the target. Leatherwood""s scope, like the others discussed above, has limited utility at long ranges because it is designed with a specific size target in mind, and would therefore be inaccurate when used with targets of widely varying size, and also because at long range the scope may not be able to move sufficiently in relation to the barrel (i.e., may be obstructed by the gun barrel).
U.S. Pat. No. 4,403,421 to Shepherd discloses a scope having a primary and secondary reticles, the secondary reticle being a polygonal reticle with different indicia on the different faces which can be rotated into position to compensate for bullet drop and determining target range for different sized targets. However, having to rotate a secondary reticle to locate an appropriate target shape in order to determine the range is time consuming and undesirable, since it takes the shooter""s attention away from the target.
It should be noted that the range finding inaccuracies inherent in these prior art references may be resolved using a laser rangefinder. However, since a laser rangefinder often emits a visible light, there is always the possibility that the beam from a laser rangefinder could be detected, revealing the position of the shooter, causing a live target to move, or other undesirable consequences, before the shot can be taken. Furthermore, a laser rangefinder includes complex electronics which must be handled with care. Laser rangefinders require highly reflective or broadside targets to achieve range. Finally, a laser rangefinder must be powered with electricity from a source which must be carried by the shooter. The additional weight is a burden, and the possibility exists that power source could fail or become exhausted through use, causing the rangefinder to cease working.
Accordingly, the need exists for a telescopic gun sight having a reticle which includes an optical rangefinder which permits a skilled shooter to rapidly and accurately identify the range to any target of estimable size, no matter how large or small, to make fast and accurate adjustment for bullet drop and windage, using the shooter""s knowledge and experience and without the need to move rings or make adjustments to the scope, thus enabling the shooter to accurately hit targets at any range, depending upon the eyesight of the shooter and the maximum range of the selected firearm.
In one embodiment, the present invention provides an improved telescopic gunsight having a housing, including a means for mounting the housing in a fixed, predetermined position relative to a gun barrel, an objective lens mounted in one end the housing, an ocular lens mounted in the opposite end of the housing, a reticle mounted in the housing between the objective lens and the ocular lens, the reticle having an optical center, a primary vertical cross-hair intersecting the optical center of the reticle, a primary horizontal cross-hair intersecting said primary vertical cross-hair at a position above the optical center when the housing is mounted to the gun barrel, to form an upper right quadrant, an upper left quadrant, a lower left quadrant, and a lower right quadrant, a plurality of secondary horizontal cross-hairs evenly spaced along the primary vertical cross-hair, a plurality of secondary vertical cross-hairs evenly spaced along at least some of said secondary horizontal cross-hairs, and rangefinder markings positioned in one of the quadrants. The telescopic gunsight of this embodiment can be a fixed power scope or a variable power scope. When optics are mounted in the housing to permit the power to be varied along a predetermined range, the reticle is most preferably mounted between the objective lens and the variable power optics.
In another embodiment, the present invention provides a reticle for use in any conventional telescopic gunsight, whether such telescopic gunsight is a fixed power scope or a variable power scope. A reticle of this embodiment is preferably constructed from an optically transparent wafer or disc having an optical center which coincides with a center of a field of vision when the wafer is mounted in a scope. A primary vertical cross-hair having a predetermined thickness bisects the disc, intersecting the optical center of the disc. A primary horizontal cross-hair having a predetermined thickness intersects the primary vertical cross-hair, most preferably above the optical center of the disc, to form an upper right quadrant, an upper left quadrant, a lower left quadrant, and a lower right quadrant. A plurality of secondary horizontal cross-hairs having predetermined thickness are evenly spaced along the primary vertical cross-hair. Preferably, at least some of these secondary horizontal cross-hairs are identified with a unique identifier, to aid the shooter in calibrating the horizontal cross-hairs by range and in locating the appropriate horizontal cross-hair to use in selecting an aiming point. A plurality of secondary vertical cross-hairs having predetermined thickness are evenly spaced along at least some of said secondary horizontal cross-hairs to aid in making accurate windage adjustments. Finally, a separate range-finding means can be positioned in one of said quadrants to aid the shooter in determining the range to target.
The present invention can also be adapted for use in a mid-range telescopic gunsight. A mid-range reticle, almost identical to the long-range reticle described above, can be constructed in accordance with this invention. Since the mid-range reticle requires less lower field area, the primary horizontal cross-hair can be conventionally centered. The mid-range reticle can then be calibrated and used in the same manner as a long-range reticle.
The reticle can also be provided with a circumscribing ring visible through the gunsight, to aid in centering the eye relative to the telescopic gunsight. This ring helps reduce shooting inaccuracy caused by the misalignment of the shooter""s line of sight through the scope. By providing a visual means to align the reticle within the scope, the shooter can produce more accurate and more repeatable results.
The reticle can also be provided with an aiming/centering dot located at the optical center of the reticle for rapid acquisition of a target at medium range, and for aiding the shooter in centering his eye relative to the field of view.
In yet another embodiment, a portion of the primary vertical cross-hair or the primary horizontal cross-hair can be provided with rangefinder markings to eliminate the need for a separate rangefinder in one of the quadrants formed by the primary vertical and horizontal cross-hair.
In yet another embodiment, the reticle can be calibrated automatically by using a computer containing a ballistics program which receives information regarding external information (such as temperature, relative humidity, barometric pressure, wind speed, wind direction, slope of the ground over which the bullet will travel, target speed, and range to target) and information regarding the weapon and bullet used (type of scope/reticle, distance of scope above gun barrel, bullet weight, ballistic coefficient of bullet, muzzle velocity of cartridge, range at which weapon was zeroed). The output of the program can be selected to produce a targeting grid for calibrating a reticle of the present invention, or for providing aiming point information for a specific target at a known range, whether the scope/reticle is a conventional scope/reticle in which the scope is adjusted to hit a target at range by rotating horizontal and vertical adjustment knobs the calculated number of xe2x80x9cclicksxe2x80x9d or whether the scope contains a reticle of the present invention in which the specific aiming point for the target is identified by reference to the calibrated secondary horizontal and vertical cross-hairs.
Other embodiments will be evident from a consideration of the drawings taken together with the detailed description of the invention.